I. Field of the Invention
The invention herein relates to pipe, particularly plastic pipe, and more particularly to coupling sections for such pipe.
II. Description of the Prior Art
Flexible couplings have been disclosed in the prior art for purposes of connecting misaligned plumbing for liquids or gas, for shock absorption, and for providing flexibility when the connections to which the coupling is attached are not rigidly fixed with respect to each other. Flexible couplings are of particular interest in earthquake-prone areas where it would be desirable to have substantial flexibility in water and other fluid lines and also where rapid repair of damaged pipes is required. All of the prior art devices rely on a corrugated section of either metal or plastic pipe to create a flexible bellows.
The primary disadvantages of the corrugated sections of flexible couplings are that turbulence and pressure drops are induced in the flow of fluids due to the irregularity of the pipe's inner diameter. Also, the corrugated ridges provide locations for solids suspended in the fluid to precipitate, with precipitation enhanced by turbulent flow. Build-up of sediment within the ridges will eventually restrict flow through the section. Such build-up is particularly undesirable in drains and supply lines where bacterial growth may be encouraged by the sediment. For example, high purity water supplies for electronic component manufacturing plants must be designed with a minimum of blind ends and irregularities in the lines where bacteria can multiply, bacteria being a source of particulate contaminants. In common household drain lines, organic material which settles in the ridges can decay and emit unpleasant odors. In sprinkler lines, dirt can accumulate, impeding water flow.
U.S. Pat. No. 3,549,176 discloses a flexible bellows joint which includes a solid liner to provide a smooth inner surface. The liner consists of an open mesh woven wire braid which is fixed at one end of the bellows, permitting the liner to slide within the bellows as the bellows is flexed. Such a device, while providing smoother flow, does not have an integral inner surface which eliminates the chance of sedimentation, and actually enhances the risk of bacterial growth by providing access via the movable end of the liner to a stagnant chamber between the liner and the bellows' inner walls. Also, once the joint is expanded, the wire mesh liner is unlikely to resile into the smooth configuration it had before it was stretched if it should be necessary to straighten or re-bend the joint in a different direction.